The present invention relates to image sensor arrays having multiple rows of photosensors, each row of photosensors being sensitive to a particular primary color. Such image sensor arrays are used, for example, for full-color scanning of hard-copy original images.
Image sensor arrays typically comprise a linear array of photodiodes which raster scan an image-bearing document and convert to the microscopic image area viewed by each photodiode to image signal charges. Following an integration period, the image signals are amplified and transferred to a common output line or bus through successively actuating multiplexing transistors.
U.S. Pat. No. 5,148,268 discloses a typical arrangement of a full-color image sensor array. Separate linear arrays of photosensors are arranged in parallel on a single bar, with the photosensors in each linear array being provided with a filter thereon of one primary color. The bar is caused to move relative to an original image in a scan direction which is generally perpendicular to the direction of the arrays. As the sensor bar moves along the original image, each portion of the area of the original image is exposed to each of the linear arrays of photosensors in sequence. As each array of photosensors moves past a particular small area in the original image, signals according to the different primary color separations of that area are output by one of the photosensors in each array. In this way three separate sets of signals, each relating to one primary color, are produced by the linear arrays of photosensors.
An important parameter in the design of an image sensor array is the resolution of the array, which will of course affect the quality of image signal based on an original image. One type of resolution is dictated by the physical configuration of the individual photosensors along the array: the higher the number of individual photosensors within a given unit of length along the array, the higher the possible resolution of data that may be output by the array. This xe2x80x9cfast scanxe2x80x9d or x-direction resolution is of course fixed by the size and spacing of the photosensors in the array.
Another type of resolution associated with an array is the xe2x80x9cslow-scan,xe2x80x9d or y-direction, resolution, which is the resolution of the image along the direction perpendicular to the direction of the array, which would be the direction of an original image moving relative to the array. In contrast to the x-dimension resolution, which is fixed by the physical characteristics of the array, the y-direction resolution is determined by the speed of an original image relative to the array, coupled with the integration times of individual photosensors. If the original image is moving relative to the array at a constant velocity, and the photosensor is operating at a high speed, each integration time of the photosensor will cause exposure to a relatively small area on the original image; if the integration time is longer, with each integration time an individual photosensor will be xe2x80x9clooking atxe2x80x9d a relatively larger area of the original image. In brief, the shorter the integration time of an individual photosensor in the array, the higher the y-direction resolution of the array.
As will be described in detail below, a technical complication may result where the desired y-direction resolution, which is related to the integration times in an array, is different from the inherent x-direction resolution of the array. For example, one possible design for a full-page-width full-color array provides, by virtue of its photosensor size, a fixed 400 SPI resolution in the x-dimension, but can provide, by virtue of the operational speed of the photosensors, a 600 SPI resolution in the y-direction. The present invention is directed to physical and operating parameters of a full-color scanning array which overcomes certain design requirements caused by high y-direction resolution.
U.S. Pat. No. 5,148,268, referenced above, and U.S. Pat. No. 5,543,838 disclose multiplexing systems for reading out signals from a full-color image sensor bar having three linear arrays of photosensors, each linear array having a filter thereon for one primary color.
U.S. Pat. No. 5,519,514 discloses a full-color sensor bar having three parallel arrays of photosensors, each array being sensitive to a different primary color. With each scan cycle as the bar is moved relative an original image, the exposure of the photosensors is precisely timed so that the optical xe2x80x9ccenter of gravityxe2x80x9d for each exposed area in the original image is superimposed for all of the primary color photosensors.
U.S. Pat. No. 5,550,653 discloses a full-color input scanner, which is operated in a mode adapted for efficient scanning of documents with simple color relations. Three linear arrays of photosensors, each linear array corresponding to one primary color, are moved relative to the original image. One linear array of photosensors operates on a full cycle and converts every single scan line of the original image into digital signals. Simultaneously, the other primary-color-sensitive linear arrays operate on half cycles and record only signals corresponding to an evenly-distributed subset of small areas of the original image.
According to one aspect of the present invention, there is provided a method of operating an image sensor for deriving image data from an original image on a sheet. There is disposed on the image sensor a first linear array of photosensors, a second linear array of photosensors, and a third linear array of photosensors, the second linear array of photosensors and the third linear array of photosensors being parallel to the first linear array of photosensors. The second linear array of photosensors is disposed between the first linear array of photosensors and the third linear array of photosensors. The sheet is moved at a predetermined velocity relative to the image sensor, in a process direction perpendicular to the first linear array of photosensors. As the sheet moves relative to the image sensor, image data from the first linear array of photosensors, the second linear array of photosensors, and the third linear array of photosensors is periodically recorded, whereby for a small area on the sheet, the image data related to the small area is recorded by the second linear array of photosensors before the image data related to the small area is recorded by the first linear array of photosensors or the third linear array of photosensors.
According to another aspect of the present invention, there is provided an image sensor for deriving image data from an original image on a sheet. A first linear array of photosensors and a second linear array of photosensors is disposed parallel to the first linear array of photosensors, each photosensor in the first linear array of photosensors and the second linear array of photosensors having a predetermined length along a process direction perpendicular to the first linear array of photosensors. A center of a photosensor in the first linear array is spaced from a center of a photosensor in the second linear array along the process direction by 14/9 a length of a photosensor in the first linear array along the process direction.
According to another aspect of the present invention, there is provided an image sensor for deriving image data from an original image on a sheet. A first linear array of photosensors and a second linear array of photosensors is disposed parallel to the first linear array of photosensors, each photosensor in the first linear array of photosensors and the second linear array of photosensors having a predetermined length along a process direction perpendicular to the first linear array of photosensors. A center of a photosensor in the first linear array is spaced from a center of a photosensor in the second linear array along the process direction by 10/9 a length of a photosensor in the first linear array along the process direction.